The first phase of Sanya’s municipal tunnel construction has kicked off. This phase includes sections with a total length of 8.1km along Shengli Road and is scheduled for completion in August 2017. The completion time for all phases of this PPP + EPCO project is 24 months and will bring water, sewage, and gas pipes, as well as power lines and communication cables together in one easily accessible subterranean service tunnel. The project is commissioned by the Sanya Housing and urban-rural construction bureau.
 


The municipal tunnel consists of two parts, a control center and the tunnel structure. The tunnels are built at a depth of 7-8 meters, with a width of 4.55 meters, and an inner diameter of 4.55 meters. The height inside the tunnel is 4 meters, and the wall thickness 0.45 meter. The tunnel corridor is built cast in-situ and has design life of 100 years. To ensure the stability of the excavation during the building of the tunnel structure sheet pile walls are driven. These water tights retaining walls are extracted and re-used in a roll-over construction path.
 


The construction area is located in an alluvial plain, which is characterized by denuded wavy plain and the bedrock is granite. Steel sheet pile construction is difficult due to the silty clay layers: green gray, gray hard plastic ~ hard and some pockets of quartz sand. The soil profile is further complicated by its unevenness which forces the sheet pile driving companies to employ a range of equipment and methods to accomplish the job. CPT values derived from the standard penetration test show N-values in the range of 3 to 28 with an average value of 22.7.
 


ICE is a foundation specialist and had a number of different hammers working on the project. The first ICE 416L vibratory hammer rolled off the production line 40 years ago this popular model is lightweight but packs 65t of driving power. The 416L was chosen to drive 16m long sheet piles each pile took 8 to 10 minutes to drive to depth. The crane hoisted 416L allowed the client to reach where an excavator piling machine has trouble reaching.
 


The excavator mounted 1223B is ICE’s most powerful, it has 67t driving force. It operates at a high frequency of 2300 rpm and requires a large excavator that can provide 327 L/ min of hydraulic flow at 350 bar working pressure. This hammer drove the 16 meter piles into the soil with 6-8 minutes sometimes assisted by pre-boring or the downward force of the excavator boom.
 


Finally, the 20RF resonance free vibratory hammer found special use in parts of the project that ran adjacent to residential areas. The variable moment of the RF hammer ensures the immediate environment does not suffer from low frequency vibrations during start-up and shut-down of the piling hammer. The 20RF offers 110t driving force and worked up to 2-meter distance from the neighborhoods houses, in some parts hugging the houses at a distance of only 50cm from the wall! The 12m long sheet piles assigned to this stretch were driven to full depth within 2-4 minutes each. Using RF technology ensured the project did not experience delay because of confrontation over potential property damage with anxious residents
 


This project demonstrated the strengths of each hammer type in trying soil conditions. Please contact ICE for advice on your specific project, we are happy to share our experience with you and make driving recommendations. Our recommendations for your soil profile can be supported by driving predictions made with ICE Wave software. We make it possible for your contractors to get the job done according to your specifications.